In typical hydrocarbon recovery completion systems, the production tubing is suspended in the casing and terminates above the top perforation. By terminating the production tubing above the top perforation, such as at 100 feet or more, the cased section of the well adjacent to the perforations has a larger diameter than the cased section adjacent to the production tubing. The larger diameter of the cased section adjacent to the perforations severely reduces the velocity of the production liquids exiting the perforations, which in turn may create liquid loading, a situation where the liquids settle at the bottom of the casing because the velocity is not sufficient enough to lift the fluids. Often, extremely long perforated casing intervals, sometimes 3,000 feet or more, are exposed to longer sections of low velocities, again increasing the inevitable liquid loading phenomena.
In recent years, “dead string” completions have been embraced by many operators in order to combat the phenomena of liquid loading. The typical dead string completion consists of a perforated sub connected to the bottom of the production tubing, and a tubing extending from the perforated sub down into the perforated casing interval. The tubing extending down from the perforated sub is plugged, hence the term “dead string”, and can have a larger or smaller diameter than that of the production tubing. As such, the dead string portion essentially reduces the flow area within the adjacent casing interval, thereby increasing the velocity of the fluid flow and enhancing hydrocarbon production over the life cycle of the well.
Current dead string assemblies are also often used to introduce chemicals down hole. These chemicals, such as scale inhibitors, are delivered from the surface to the perforated sub and ultimately to the perforated casing to perform their desired function. Various techniques have been used and proposed for delivering the chemicals. For example, chemicals have been introduced by “strapping” a capillary tubing to the outer diameter of the production tubing with bands while a workover rig is installing the production tubing. The capillary tubing is coupled to a cross over sub to introduce the chemicals to the inside diameter of the dead string through a chemical injection valve and, hopefully, out into the annulus between the dead string and the casing to treat the well across the entire perforated interval.
Presently known techniques for providing chemicals (or any other desired liquids, gasses, equipment or a combination thereof) via a dead string completion assembly may have one or more drawbacks. For example, it may not be possible to snub the well live due to the capillary string and bands (i.e., strapping) on the outer diameter of the production tubing. In such instance, in order to accommodate the strapping of the capillary tubing to the production tubing, the well must be killed and heavy hydrostatic fluids, which may cause damage to the formation, may need to be used. For another possible example, should the capillary become plugged or the chemical injection system become inoperable, the well must be killed again in order to pull the entire production string for repair and/or replacement of the capillary line. For yet another potential example, in the case of backside capillary lines, the strapped capillary must penetrate the tubing hanger—which can be a costly endeavor.
It should be understood that the above-described discussion is provided for illustrative purposes only and is not intended to limit the scope or subject matter of the appended claims or those of any related patent application or patent. Thus, none of the appended claims or claims of any related application or patent should be limited by the above discussion or construed to address, include or exclude the cited examples, features and/or disadvantages, merely because of the mention thereof above.
Accordingly, there exists a need for improved systems, apparatus and methods capable of injecting any desired fluid(s) or inserting equipment into a subterranean well through a dead string completion assembly having one or more of the attributes or capabilities described below or evident from the appended drawings.